log1p

接口定义

C interface：

float log1pf(float x);

double log1p(double x);

long double log1pl(long double x);

参数

返回值

• 返回以e为底1+x的对数函数值y，y ∈ (-INF, +INF)。
• 输入x为+0，返回+0。
• 输入x为-0，返回-0。
• 输入x为-1，返回-∞。
• 输入x为+∞，返回+∞。
• 输入x<-1，返回nan。
• 输入x为nan，返回nan。

依赖

C: "km.h"

示例

C interface:

    // typical usage
    double x1 = 0.0, x2 = -0.0, x3 = -1, x4 = -2;
    // special handing
    double a = INFINITY, b = -INFINITY, c = NAN;
    // print result
    printf("log1p(0.0) = %.15f\n", log1p(x1));
    printf("log1p(-0.0) = %.15f\n", log1p(x2));
    printf("log1p(-1) = %.15f\n", log1p(x3));
    printf("log1p(-2) = %.15f\n", log1p(x4));
    printf("log1p(INFINITY) = %.15f\n", log1p(a));
    printf("log1p(-INFINITY) = %.15f\n", log1p(b));
    printf("log1p(NAN) = %.15f\n", log1p(c));

    /* 
     * log1p(0.0) = 0.000000000000000
     * log1p(-0.0) = -0.000000000000000
     * log1p(-1) = -inf
     * log1p(-2) = nan
     * log1p(INFINITY) = inf
     * log1p(-INFINITY) = nan
     * log1p(NAN) = nan
     * 
     * */